Indirectly heated oven



W. `VAN GUILDER INDIRECTLY HEATED ovEN Filed July 22, 1940 Jan. 18,1944.

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INDIRECTLY HEATED OVEN Filed July l:22, 1940 2 V'sheets-sheet '2OOOOOOOOOOOOOO OOOOGOOOOOOOOO OOOOOOOOOOOOOO @OOOOOOOOOO O O O OPatented Jan. 18, 1944 I i 'INDIRECTLY HEATED OVEN Walter Van Guilder,River Forest, I'Ill., assigner to Precision Scientific Company, Chicago,111.,

a corporation of Illinois Application 'Jury 22,1940, serial No.3416.759V

claims. (c1. 263-42) The invention relates primarily to indirectlyheated ovens such as are used, for example, for sterilization. Byindirectly heated" is meant an oven of the type in which the air withinit has no actual contact with a gas burner or other combustion typeheater for the oven but is instead warmed by radiation and conductionthrough an imperforate wall or the like so that there is no possibilityof products of combustion from the heaterentering the oven chamber.

One object of the invention is to provide an oven of the type indicatedwhich has a materially higher elciency and more evendistribution of heatthroughout the oven than vcould be obtained with ovens of this generaltype heretofore available.

Another object is to provide such an yoven which is characterizedparticularly by the-free and naturalconvection oW of both the indirectlyheated air in the oven chamber itself and of the directly heated air andproducts of combustion from the burner. v

Still another object is to provide such an oven in which a novelarrangement and construction of thefparts'accomplishes aV rugged andeilicient structureat quite low cost.

The invention also resides in various structural improvements by meansof which the exe terior finish-on the apparatus is guarde'dagainstdamage'from the heater.

Further objects and advantages of theinvention will become apparent asthe following` description proceeds, taken in connection with theaccompanying drawings in which:

Figure 1 is a general perspective view of Van oven embodying theinvention.

Fig. Z'is an enlarged perspective view of the oven with portions of thestructure broken away to show the interior arrangement of the'parts andthe paths of air circulation.

Fig. 3 is a vertical sectional view taken substantially along the line3-3 in Fig. 2.

Fig.- 4 isa transverse sectional View taken substantially along the line4-4 in Fig. 3.

Fig. l5 is an enlarged detail perspective view of the hand holes andclosure member therefor in the lower front portion of the oven.

While the' invention is susceptible of various modifications andalternative constructions, I have shown in the drawings and will hereindescribein detailthe preferred embodiment, but it is to be understoodthat I do not thereby intend to limit the invention to the' specificform disclosed, but intend to cover all modifications and alternativeconstructions falling Within the manner hereinaftrfdescribed YThe'innerlshell III defines y.the ovenv chamber C and .articles 'to betreated are supported-,in it on Ysuitable .open

Work Shelves` I3(Flg. y1) removably in'bunte-d-llllA brackets; la nxed.to the'inner'raicesv of theisneu. The inner' shell I'I is simply arectangular slfie'etf metal vbox comprising top, bottomrearand'end wallsI5, |56', IT, I8' and I9, respectively. v"llh'e.. front wall of theshellII is, of course, open and. isA arranged to beclosed by the`doorAII'IfIFigs. Zand 3).. A flangel is bent up from the" front-edgeof.l thetop wall I'B-and constitutes the exterior front portion of the cabinetabove the door. e

The outershell I2 ofthe cabinet .is.of'-'double Walled construction and,ineeifect, comprisesinff. ner and outersheet `metal shells with thermalinsulatingV material y2 -I between vthem .(Fig. l 2)". Thus the-end andlrear-walls of thecabinetfarq. formed by nested sheet metal shells 22land 2'3- with-the*insulating-material between them. e i'jlhe forwardedge portions'Y Iof vthesej shellsv are-bent around tol form they yfrontwall portions oil-the' cabinetl attheV side edges 0f the door IIl` (seeFig. l). The stop of the outer'shell I2 isfformeda doublefwalledremovable cover structure -24 with the insulatingmaterial 2 Iy betweenits walls: .,:A sheet` metal plate'25 (seeFig. 2) constitutes'lthebottom'walloftlieotershell I2. .n Th'einn'erf and y outer shells- I Iand I 2. are together at th'eiri frontpo'rtions.` Thus, atthe top" of'fthe structure the angelZ 0'. on'. the inner` shellh I Il isjoinedat'-fto ,the adjacentlfrort 'ila'n lori' theoutersecnon'zs' of theshell I2. smiianyf in tneiowr .portion of the cabinet .thelbo'ttom'wausf I`6arid. 25,'.of1th`e'inner` and outer shells I VIan'd I2,.respectively, are iixed to tlie Hanges of. ach'annell2lf e l e Heating'.'0fthe ovencnamber C is accomplished; in'ktl'iefpresetinstance,byf'mnsof'al gas blrleI 23 k,(liig's( 2` .andl3l rikbi-terios'`ed`betweenv the" shell" bottoni Wallsll- -and725, res'p'ectiv'ely.`,Th-elburner shownI is of conventional forni and`c'oniprises2,n

and I9 of the innershell, as indicated by the ar`u^ rows 3| in Fig. 2.Thereafter these hot gases.

wash over the top wall I5 of the inner shell and are finally dischargedthrough a Vertical'ilue 32Y set into the cabinet top 24.` As: these hotgases x wash over the back and top walls of the inner shell, furtherheat is transferred to the interior of the latter so that, in all, theheat 'generated by the burner 28 is finally transferred with a highdegree of efficiency to the inner oven chamber C.

Secondary air for the' burner 28 is supplied througha series of holes 33in the outer shell bot- .tom wall which underlies the burner (Figs. 2and 4). In connection with the layout of holes in the bottom wall 25 itshould also be noted that desirably two large apertures 34 are arrangedin its rear corner portion to underlie the rear corners of the innershell II Additional cool air is `admitted throughoutthese holes'34 and,being mingled withthe rising products of combustion, washes over thevertical edge portions of the innerxshell' at its rear corners.' This isdesirable inrorder to enhance the uniformity of temperature within theoven vchamber C. In this connection it will be observed, upon a study ofthe construction that heat is supplied to the portion of the chamber Cadjacent its'rear cornersY from, both the end Walls andback wall.Consequently, unless someprovision, sucl'ras holes 34, isprovided forreducing somewhat the temperature of theair surrounding the rear edgesVof the inner shell (as comparedl to that' washing over the centralportions of the 'endA and side walls) the area of' the chamber Cadjacent'its rear corners will beoverheated. By diluting the rising hotgases atv the points'noted, with cool air through the holes 34, thistendency to overheating at the rearV corners is effectually overcome. YTo define 'an-entrance throat 35 V(Fig-2) for the admission ofy freshair to the oven member C,- the channel 21 `is setback somewhat from thefront ofthe cabinet-,and is overlaid in spacedv relation by a frontpanel 36. Fresh air rises through tliis entrance passage 35 between themembers 36 and 21; and Hows into the chamber C'where itis warmed by heattransmitted through-- the walls of the inner shell I I.

To' diffuse the entering air uniformly throughout the oven'chamber C andalso to insure uniformity of heating ofthe same, prior to its entryAinto the chamber proper, arbafiie arrangement is provided. For thispurpose an apertured'bafile plate 31 is used, the front panel 36V being,incidentally, an"integral front flange on` this plate. Furthermore,asecond baille plate-33 is arranged in spaced relation beneath the frontportion of thebaiiie'plate 31. Thus airl entering through the passage 35ows rearwardly over the upper lsurface of the` bottom plate I6 where itis warmed by heat transmitted through this plate from the burner. Asshown, the plate 31 is spaced a short distance above the bottom walld I6Vof the oven chamber. Part of the entering airflows upwardintofthelchamber C through holes 38 in the rear portion of the plate 31while the rest of the air flows back over the edge of the inner baffle31 and up through the holes 39 in the front portion of the plate 31, allas indicated by the arrows 4I) (Fig. 2).

To insure a circulation of air through the oven chamber C, the velocityhead of the products of combustion leaving the flue 32 is used toentrain air from the oven chamber and induce a flow through it. For thispurpose an outlet conduit 4I is provided in the top of the inner shellII (Figs. 2 and 3), this outlet 4I being arranged to project up throughthe center of a' brackets 43.

Particularly to be noted is the fact that the path of circulation forair through the oven chamber C is such that ther entrainment effect ofthe products of Vcombustion in the ue 32 augments the natural convectionnow of 'air through the oven chamber. In other words, the air movesupward through the oven chamber in a direction which would be normalfor'convection flow alone and the entrainment of the air escaping fromthe oven chamber simply augments or increases this natural ilow. Inthevsame connection it should be noted that the owgfof products ofcombustion and directly heated air between the inner and outer shells'II and I2 is also always in the direction for normal convection flow,or, in other words, generally upwards to atmosphere, so that there is notendency to impede or retard this natural flow and -to`trap the productsof combustion in isolated hot pockets.

Access to the burner 28 for lighting, etais afforded through registeringhandholes 44 and 4 5 formed in the low front portion of the cabinet inthe front panel 36 and channel 21, respectively (Figs. 2 and 5). Thesehand holes are normally closed by a closure member 46 of box formpivoted at 41 to swing between the opposed faces of the members 36 and21. A handle or pin 48 for swinging the closure member projects throughthe front hand hole 46. In connection with the construction of thisportion ofthe apparatus it shouldsalso be noted that the location of theair intake passage 35 behind the front panel 36 efectually protects theenamel finish on the latter from overheating due to the proximity of theburner 28. The channel 21 itself, as well as the layer of cool enteringair in the inlet 35 form an eective barrier against the transfer of anexcessive amount of heat to the panel 36.

In using the oven described, the operator opens the valve 30 and reachesin through the hand holes 44, 45 to light the burner 28. Then theclosure member 46 is restored to its closed position and the oven isheated until the chamber C reaches a stable temperature of, for example,some desired point between 200 to 450 Frsuch as is used insterilization. A thermometer (not shown) inserted in a thermometer well50 in thetop of the oven (Fig. 2) serves to indicate the ing iscontinued for a desired period requisitev for proper sterilization.During this heating the hot products of combustion from theburner Q28lrise about the exterior of the inner shell l l, as described above, andescape through the flue 32. Fresh air entering the inlet 35 passes intothe oven chamber, being heated from the hot bottom wall l of the innershell Il, which directly overlies the burner 28, and is distributed bythe baffle structure 3l, 38. Further heat is, as previously described,transmitted to the air in the oven chamber through the rear, end and topwalls of the inner shell Il. The warmed air within the oven chamber Crises to the outlet 4l where it is entrained by the escaping products ofcombustion so that a uniform circulation of air takes place Within theoven chamber. This system of operation insures not only a very highdegree of efliciency for ovens of this type but also has been found toinsure great uniformity of temperature throughout the oven chamber.

I claim as my invention:

l. An oven comprising, in combination, two generally rectangular sheetmetal shells nested together with top, bottom, end and back walls inspaced relation, the registering fronts of said shells being open, thefront edges of said bottom walls being set back from the front edges ofsaid top walls, a sheet metal panel extending between said front edgesof the bottom wall and rigid with the same, an apertured diffuser plateoverlying in spaced relation the bottom wall of said inner shell andhaving a downturned front ange spaced forwardly from said panel to denean air inlet passage into said inner shell beneath said diffuser plate,said flange being joined at its ends to said outer shell to form a frontfinishing panel for the lower portion of the structure, and a heaterlocated between said shell bottom walls, the air in said inlet passageserving to form a heat insulating barrier between said heater and saidnishing panel.

2. An oven comprising, in combination, two generally rectangular sheetmetal shells nested together with top, end and back walls in spacedrelation, the registering fronts of said shells being open, said innershell having an upturned flange on the front edge of its top wall joined:to the outer shell at its ends and forming a front nish panel for theupper portion of the front of the structure, said inner shell having animperforate bottom wall with its front edge set back from the front edgeof its top wall, an apertured diiuser plate overlying said bottom wallof the inner shell and spaced above it, said diuser plate having adownturned flange along its front edge substantially flush with thefirst mentioned ange and joined at its ends to the outer shell to form asecond nishing panel for the lower front portion of the structure, avertical panel depending from the front edge of said inner shell bottomwall in spaced relation behind said Second finishing panel to define anair inlet into said inner shell beneath said diffuser plate, and aheater beneath said bottom Wall of the inner shell and behind saidvertical panel.

3. An oven comprising, in combination, a cabinet structure having aliner therein dening an oven chamber with an inlet opening extendingalong an edge oi the bottom of such chamber, said cabinet having aportion of its outer wall extending downward from the outer edge of saidinlet opening, a panel extending downward from the inner edge of saidinlet opening and coacting with said por-tion of the cabinet Wall todene an air inlet channel open at its lower end and leading into saidinlet opening, and a heater beneath said chamber and behind said panel,the blanket of fresh air in said channel forming a heat insulatingbarrier between said heater and said portion of the cabinet wall toprotect the latter from overheating.

4. An oven comprising, in combination, a generally rectangular outercabinet with an inner liner therein defining an oven chamber, saidcabinet having a door opening in a side wall thereof for access to saidchamber, said chamber having an air inlet opening in its bottomextending along just inside said door opening, a vertical panel beneathsaid liner spaced inward from the adjacent portion of the cabinet wallbeneath said opening and coacting therewith to form an air inlet passageto said inlet opening, a heater beneath said liner, said panel andportion of the cabinet wall having registering hand holes therein togive access to the heater, and means forming a closure unit for closingboth of said hand holes.

5. An oven comprising, in combination, an outer cabinet with an innerliner therein dening an oven chamber, a heating unit beneath said liner,said liner having an air inlet opening in its bottom adjacent one sideedge of the latter, an apertured diiTuser plate overlying the bottom ofsaid linerin spaced relation to it, and a baille interposed in spacedrelation to both said difi'user plate and bottom of `the liner, saidbaiile overlying said opening and only a portion of the bottom of theliner.

WALTER VAN GU'ILDER.

